Receptors for the Fc portion of IgG (FcRGamma) mediate recognition of antibody-labelled particulate antigens by monocytes, macrophages and neutrophils. Thus, FcRGamma play a beneficial role in clearing the body of immune complexes, viruses, bacteria, and perhaps malignant cells. For clearance to occur, several molecular events must follow recognition of opsonized particles fo FcRGamma, a sequence of events that is poorly understood. To enhance our understanding of these molecular events, we propose to study the mechanisms that govern the generation and modulation of transmembrane currents in single human monocytes and monocyte-derived macrophages. Macrophages have recently been shown to exhibit voltage-dependent ion conductances, and FcRGamma have been shown to be agonist-activated ion channels. Through the application of electrophysiological techniques, membrane conductance changes will be measured in relation to macrophage effector activities. The objectives are (1) to measure the voltage sensitivity of single channel conductance systems, (2) to establish the ion selectivity of single channels, (3) to investigate agonist activation of single channel currents and (4) to seek evidence for a second messenger activation mechanism for single channel events. Channel characterization will be carried out using the membrane patch clamp technique. A profile of membrane channel properties will be obtained from deteminations of channel distribution, mean channel lifetime and reversal potential in response to membrane voltages clamped at various levels and in response to various agonists. Ion specificity of receptor-mediated channels will be determined by altering transmembrane ionic ratios. In addition to normal monocytes and macrophages, two human cell lines (HL-60 and U-937) will be explored with the membrane patch-electrode technique before and after treatment with immune interferon. Pure recombinant immune interferon increases both FcRGamma sites and FcRGamma-dependent functions by nearly 10-fold. Monoclonal antibodies plus flow cytometry will be used to characterize and to sort cells for high and low expression of functionally important membrane receptors. The studies we propose will thus establish electro-physiological criteria by which to evaluate membrane behavior in both the resting and interferon-activated human mononuclear phagocyte. The insights obtained during this study may lead to a better understanding of the molecular events which underlie alterations in mononuclear phagocyte function in diseases such as rheumatoid arthritis and systemic lupus erythematosus.